1. Field of the Invention
The present invention relates to purification of fatty acid alkyl esters (FAAE), in particular, biodiesel, and more particularly, to a process for quick, continuous purification of crude biodiesel by treating crude biodiesel with an adsorbent material contained in one or more columns and regenerating the adsorbent material for re-use.
2. Description of Related Art
Economically viable renewable energy has been a policy goal of governments around the world. One source of renewable fuel that has been promoted and developed is biodiesel. The attraction of biodiesel is the similar properties it possesses in relation to petroleum-based diesel fuel. Biodiesel is a desirable energy alternative to wind, solar, and ethanol derived energy in that the energy content to capital requirement is close to a break-even point, depending, of course, upon the price of petroleum derived energy.
Biodiesel is the purified alkyl esters of fatty acids generally referred to as fatty acid alkyl esters (FAAE). Production of these fatty acid alkyl esters (FAAE) is achieved by the transesterification of animal or vegetable fats or oils or the esterification of fatty acids, including free fatty acids (FFA) found in degraded fat or oil. The process involves the reaction of triacylglycerol with an alcohol, typically methanol, in the presence of a catalyst, typically sodium or potassium hydroxide or methoxide, a reaction referred to as transesterification. Alternately, fatty acids, including those found in degraded fat or oil containing high levels of free fatty acids (FFA), typically referred to as yellow grease, brown grease, or trap grease, are reacted with an alcohol, typically methanol, in the presence of an acid, a reaction referred to as esterification. When using degraded fat or oil as a raw material, esterification is performed prior to transesterification in order to provide for a complete conversion of fatty acids into FAAE. Unreacted methanol from both processes is typically removed by flash evaporation so that it can be reused for the esterification and/or transesterification reaction(s).
However, simply performing the esterification and/or transesterification of fatty acids is not enough to produce a usable biodiesel fuel. Fatty acid alkyl esters (FAAE) contain impurities that can crystallize, foul engines, and cause numerous problems for the user. As a result, regulations have been developed to address the needs of the consumer with respect to quality. Strict standards for commercial biodiesel have been developed by most countries, including the U.S. Government in the specifications set forth in ASTM International's ASTM D6751 and the European Union in the specifications set forth by the European Committee for Standardization in EN 14214.
The specifications for ASTM D6751-07a are as follows:
Biodiesel is defined as the mono alkyl esters of long chain fatty acids derived from vegetable oils or animal fats, for use in compression-ignition (diesel) engines. This specification is for pure (100%) biodiesel prior to use or blending with diesel fuel.
PropertyASTM MethodLimitsUnitsCalcium & Magnesium, combinedEN 145385maxppm (ug/g)Flash Point (closed cup) D 9393min.Degrees C.Alcohol Control (One of thefollowing must be met)1. Methanol ContentEN141100.2Max% volume2. Flash PointD93130MinDegrees C.Water & SedimentD 27090.05max.% vol.Kinematic Viscosity, 40 C.D 4451.9-6.0mm2/sec.Sulfated AshD 8740.02max.% massSulfurS 15 Grade D 5453 0.0015max. (15)% mass (ppm)S 500 GradeD 54530.05max. (500)% mass (ppm)Copper Strip CorrosionD 130No. 3max.CetaneD 61347min.Cloud PointD 2500ReportDegrees C.Carbon Residue 100% sampleD 4530*0.05max.% massAcid NumberD 6640.50max.mg KOH/gFree GlycerinD 65840.020max.% massTotal GlycerinD 65840.240max.% massPhosphorus ContentD 49510.001max.% massDistillation, T90 AETD 1160360max.Degrees C.Sodium/Potassium. combinedEN 145385maxppmOxidation StabilityEN 141123minhoursWorkmanship = Free of undissolved water, sediment, & suspended matterBOLD = BQ-9000 Critical Specification Testing Once Production Process Under Control*The carbon residue shall be run on the 100% sample.#A considerable amount of experience exists in the US with a 20% blend of biodiesel with 80% diesel fuel (B20). Although biodiesel (B100) can be used, blends of over 20% biodiesel with diesel fuel should be evaluated on a case-by-case basis until further experience is available.Source: SPECIFICATION FOR BIODIESEL (B100) - ASTM D6751-07a (March 2007).The specifications for EN 14214 are as follows:
LimitsPropertyUnitMinimumMaximumTest methodEster content% (m/m)96.5EN 14103Density at 15° C.kg/m3860900EN ISO 3675EN ISO 12185Viscosity at 40° C.mm2/s3.505.00EN ISO 3104Flash Point° C.120—prEN ISO 3679Sulfur contentmg/kg—10.0prEN ISO 20846prEN ISO 20884Carbon residue% (m/m)—0.30EN ISO 10370(on 10% distillation residue)Cetane number51.0EN ISO 5165Sulfated ash content% (m/m)—0.02ISO 3987Water contentmg/kg—500EN ISO 12937Total contaminationmg/kg—24EN 12662Copper strip corrosionratingclass 1EN ISO 2160(3 h at 50° C.)Oxidation stability 110° C.hours6.0—EN 14112Acid valuemg KOH/g0.50EN 14104Iodine valuegr iodine/100 gr120EN 14111Linolenic acid methyl ester% (m/m)12.0EN 14103Polyunsaturated (>=4 double bonds)% (m/m)1methyl estersMethanol content% (m/m)0.20EN 14110Monoglyceride content% (m/m)0.80EN 14105Diglyceride content% (m/m)0.20EN 14105Triglyceride content% (m/m)0.20EN 14105Free glycerol% (m/m)0.02EN 14105EN 14106Total glycerol% (m/m)0.25EN 14105Group I metals (Na + K)mg/kg5.0EN 14108EN 14109Group II metals (Ca + Mg)mg/kg5.0PrEN 14538Phosphorus contentmg/kg10.0EN 14107Source: European Standard EN 14214: Automotive fuels - Fatty acid methyl esters (FAME) for diesel engines - Requirements and test methods (approved on 14 Feb. 2003)
Because they are usually the most economical raw material, fats and oils are commonly used as a feedstock for the esterification and/or transesterification reaction(s) to produce biodiesel. Fats and oils commonly undergo purification to remove contaminants prior to being used as the feedstock for biodiesel and other applications. The following patents relate to the purification of fats and oils.
U.S. Pat. No. 1,745,952 discloses a method to decolorize fats and oils. U.S. Pat. No. 2,401,339 discloses a method of removing impurities from fats, oils and waxes through the use of solid adsorbents and distillation. U.S. Pat. No. 3,862,054 discloses a method of removing phosphorus compounds and free fatty acids from vegetable oils. U.S. Pat. No. 5,252,762 discloses a method to remove contaminants (free fatty acids, soaps, phosphorus, metal ions and color bodies) from glyceride oils with a base treated adsorbent. All of the above described patents are directed to the purification of the fats and oils themselves, and not biodiesel or any other fatty acid alkyl esters. While fats and oils can be used as a feedstock for the production of biodiesel, the fats and oils do not constitute biodiesel.
As a result of the above-described transesterification reaction, two products are produced: fatty acid alkyl esters (FAAE) (typically Fatty Acid Methyl Esters) and glycerin. The glycerin portion is separated from the fatty acid alkyl esters (FAAE) portion, either by centrifugation or gravity settling, and the resulting fatty acid alkyl esters (FAAE) is referred to as crude biodiesel. The crude biodiesel portion consists of fatty acid alkyl esters (FAAE) containing impurities that must be removed before it can be commercially marketed as biodiesel. These impurities include, but are not limited to, alcohol, glycerin, soaps, residual catalyst, metals, free fatty acids, sterol glycosides as well as other impurities that reduce the stability of biodiesel. Therefore, at this point in the process, the fatty acid alkyl esters (FAAE) is not considered to be biodiesel and cannot be commercially marketed as biodiesel until the proper specifications (e.g. ASTM D6751, EN 14214, and the like) are achieved.
Conventional solutions to remove impurities from a crude biodiesel and produce a product that meets relevant specifications, include water wash, ion-exchange resin, and filtration using an adsorbent powder. Some conventional methods have combined the techniques to help achieve regulatory specifications. The unreacted methanol is removed from the crude biodiesel portion either prior to the purification process or after the purification process depending on which purification techniques) are used.
U.S. Patent Application Publication No. 2005/0018143 describes a process to produce a fatty acid alkyl ester for diesel fuel using water washing to remove the impurities. After the water washing process is completed, the fatty acid alkyl ester is treated with a high-water-absorptive resin to remove the water from the fatty acid alkyl ester.
U.S. Pat. No. 4,371,470 describes a method for producing a high quality fatty acid ester by esterification process, water washing to remove impurities and using an adsorbent to remove color from the fatty acid ester. The adsorbent is described as either activated clay or a mixture of activated clay and activated carbon.
The drawbacks of water wash are the large volume of fresh water needed to treat the biodiesel, the long amount of time required to treat the biodiesel, the potential for emulsion formation and resulting waste, and the large volume of wastewater either to be disposed of or treated.
Various patents describe purification of biodiesel, esters and related chemicals using adsorbents such as clay, carbon, silicon based adsorbents, such as magnesium silicate and zeolites.
U.S. Pat. No. 6,982,340 describes a process for purifying an ester with adsorption-treating with clay/activated carbon and a hydrogenating decomposition-type adsorbent using a carrier. The adsorbents in this process are used for the removal of sulfur compounds from an ester, not biodiesel. Even though biodiesel is a type of ester, there are numerous ester compounds not associated with biodiesel.
U.S. Patent Application Publication No. 2005/0081436 describes a method by which biodiesel is purified using an adsorptive filtration process using synthetic magnesium silicate.
U.S. Patent Application Publication No. 2005/0188607 describes a system for the removal of methanol from crude biodiesel using adsorptive filtration with a silicon based adsorbent (e.g. magnesium silicate). The removal of glycerin, and sodium or potassium hydroxide is also included.
U.S. Patent Application Publication No. 2006/0260184 describes an apparatus and process to refine biodiesel fuel through the use of an adsorbent material (e.g. magnesium silicate). This process also uses filtration.
U.S. Pat. No. 5,401,862 describes a process for the decolorization of fatty acid esters particularly the fatty acid esters suitable for use in foods and cosmetics. A solution of fatty acid ester dissolved in a polar solvent is passed through a column containing an adsorbent (mixture of montmorillonite clay and group consisting of silica gel and activated carbon). The solvent is then eliminated from the ester. The only contaminant claimed to be removed from this process is color.
U.S. Pat. No. 4,049,688 describes a method by which saturated esters of fatty acids can be separated from unsaturated esters through use of selective adsorption using an X or Y Zeolite.
The major drawback of adsorbent treatment of biodiesel is the disposal of the spent adsorbent filter cake.
None of these patents describe a continuous process using column purification or adsorbent regeneration. It is desirable to provide a continuous process for the purification of biodiesel. It is further desirable to provide a process that once charged with adsorbent comprises a closed system requiring no fresh water or new adsorbent for operation and generating no waste water or solid waste that needs to be treated or disposed of. Such a system is both economical and environmentally friendly.
A regenerable column adsorption system has been described. U.S. Pat. No. 6,635,595 describes a process for simultaneous alkyl esterification of edible oil and regeneration of spent oil purification medium. The process includes the simultaneous regeneration of spent clay and in situ recovery of oil from spent clay and conversion of the same to alkyl esters by treating the spent clay with alcohols. The process treats a mixture of spent clay (which contains residual oil from the edible oil refining processes) and vegetable oil such that the clay can be regenerated at the same time the oil is converted into alkyl esters. After this process, the regenerated spent bleaching earth is further activated at 120-500° C. for 2-6 hours so that it can be reused for the bleaching of vegetable oils (in refining process). The regeneration of the clay adsorbent material is described in this patent such that it could be reused in the vegetable oil refining process, but not in biodiesel purification.